Mutations That Alter Circadian Rhythms of Behavior in Zebrafish

Gregory M. Cahill

Department of Biology and Biochemistry, University of Houston, Houston, TX

Circadian clocks regulate many aspects of behavior, including sleep-wake cycles, sensory function, and reproduction. Genes that code for circadian clock components have been discovered by screening a variety of model organisms for mutations that alter the period or amplitude of circadian rhythms. We have initiated a behavioral screen for clock mutants in zebrafish in an effort to identify new vertebrate circadian clock genes and to gain insight into the functions of known clock genes. Our primary screening assay is the circadian rhythm in spontaneous swimming activity of 9-18 day old larvae, measured by an automated infrared video image analysis system. We are screening for dominant mutations that alter the timing of behavioral rhythms in the progeny of ENU treated males crossed with wild-type females. We recovered two confirmed clock mutants from the first 1275 animals tested. Both of these mutant alleles are incompletely dominant, shortening the freerunning period of behavioral rhythms by 0.5-0.8 h in heterozygotes and 1-1.5 h in homozygotes. One of the mutations maps to Linkage Group 7 and the other maps to LG 20. We have so far confirmed that one of these mutations also shortens the period of the melatonin release rhythms measured from cultured pineal glands, indicating that the mutant gene product affects tissue-level rhythmicity as well as behavior. We are continuing to screen for new mutants in order to identify additional alleles of these genes, as well as mutations in other vertebrate clock genes. Our experience so far indicates that the zebrafish will be a productive model system for genetic analysis of the biological clocks that regulate vertebrate behavior.